When such belts are used for transmitting high power, proposals have already been made to increase their transverse stiffness by inserting reinforcement in the teeth, said reinforcement extending across the belt. Such proposals can be seen, for example, in SU-A-1 033 794, or EP-A-0 084 702, or in EP-A-0-222 637 in the name of the present Assignee. SU-A-1 033 794 describes a toothed belt in which a metal strip is embedded in the resilient matrix constituting the belt for the purpose of reducing vibration and noise, said strip being shaped by stamping in order to present pairs of lugs which are disposed to correspond with the teeth of the belt. The lugs are kept in place and held by hollow transverse inserts which are received in the teeth between adjacent lugs, thereby considerably reducing longitudinal flexibility and consequently giving rise to rapid damage in operation by loss of cohesion at the interfaces between the inserts and the resilient matrix, in spite of adhesion means being provided to ensure said cohesion.
Although belts as described in EP-A-0 222 637 in which reinforcement is received in the teeth extending substantially transversely relative to the belt, said reinforcement being generally "open" in cross section rather like guttering, do indeed give satisfaction, it would nevertheless be desirable to further improve the characteristics of such belts in particular with reference to their flexibility so that they can be passed around the small-diameter pulleys with which they may need to co-operate.
Thus, a general object of the present invention is to provide an improved power transmitting toothed trapezoidal belt which has excellent winding deformation characteristics, including characteristics enabling it to wind about small-diameter pulleys with which it may be required to co-operate, and which also has teeth having excellent stability in the radial plane while enabling high power to be transmitted, i.e. while having the required transverse stiffness without thereby preventing it from having longitudinal flexibility.
Another object of the invention is to provide such a belt having an operating lifetime which is as long as, if not longer than, the lifetime provided by prior art belts, and which also avoids the drawbacks of some prior art belts in which transverse stiffness is obtained by means of inserts provided in the teeth of the belt.